The Southern Poverty Law Center (SPLC) is again hassling conservatives with whom it doesn’t share a worldview.

The SPLC’s latest victim is the David Horowitz Freedom Center, a conservative think tank whose emphasis is public policy and institutional reform. It’s based in Sherman Oaks, California.

“The David Horowitz Freedom Center stated in a recent email that its ability to accept donations by credit card has been disabled by both Visa and Mastercard following a campaign by SPLC to label the Freedom Center as a hate group,” according to a report by Breitbart.

“This blow could be the end of the Freedom Center. Decades of work, down the drain because the hateful Left wants to squash free speech and silence an organization that dares to question them,” reads an email from the Freedom Center to supporters.

David Horowitz (shown above right, at the top of this article), the organization’s founder, is also the best-selling author of “Big Agenda: President Trump’s Plan to Save America.”

“We have been attacked by the left-wing hate machine whose goal is to suppress and silence conservative voices,” said Horowitz in a statement to Breitbart. “This is the work of a Soros-funded Media Matters and Southern Poverty Law Center operation.”

He continued, “It’s cynical, calculated and supported by the Democratic Party. The reason Mastercard and Visa gave us for cutting us off and thus sabotaging our online fundraising operation is that the SPLC told them that we were a hate group. It is wrong to focus on the tech heads as the culprits because as businessmen they have a vested interest in keeping their platforms politically neutral.”

Horowitz continued, “They have been threatened by Sen. Mark Warner and other Democrats if they don’t censor conservatives. The fact that Mastercard and Visa are now part of this juggernaut indicates how dangerous this has become.”

LifeZette reached out to Visa but did not hear back by publication time.

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“We can’t process donations from any major credit card companies [now],” also Horowitz wrote in an email, according to The Daily Wire.

In a unsettlingly similar scenario back in May, Amazon, the world’s biggest online retailer, based in Seattle — and the owner of The Washington Post, ironically — dropped Alliance Defending Freedom (ADF) from its charitable giving program, called Amazon Smile.

Based in Scottsdale, Arizona, ADF is a conservative nonprofit that defends religious liberty, the sanctity of life, and marriage and family, both nationwide and around the world.

ADF is the group that successfully argued on behalf of Colorado cake artist Jack Phillips in the June case Masterpiece Cakeshop v. Colorado Civil Rights Commission before the Supreme Court.

Horowitz is justified in decrying the SPLC, which has been the subject of several blistering op-eds from high-profile publications.

A Wall Street Journal op-ed by Jeryl Bier, titled “The Insidious Influence of the SPLC,” noted how that organization flagged the Washington, D.C.-based Family Research Council (FRC) as a hate group for advancing “faith, family, and freedom in government and culture from a Christian worldview.”

“Aided by a veneer of objectivity, the SPLC has for years served as the media’s expert witness for evaluating ‘extremism and ‘hatred,'” noted the op-ed.

Related: Not OK for Feds to Weaponize SPLC List to ‘Attack Citizens’

“But while the SPLC rightly condemns groups like the Ku Klux Klan, Westboro Baptist Church and New Black Panther Party, it has managed to blur the lines, besmirching mainstream groups like the FRC, as well as people such as social scientist Charles Murray and Somali-born Ayaan Hirsi Ali, a critic of Islamic extremism.”

Even The Washington Post had similarly harsh words for the SPLC.

“After years of smearing good people with false charges of bigotry, the Southern Poverty Law Center (SPLC) has finally been held to account,” wrote columnist Mark A. Thiessen in a June op-ed for The Post.

“A former Islamic radical named Maajid Nawaz sued the center for including him in its bogus ‘Field Guide to Anti-Muslim Extremists,’ and this week the SPLC agreed to pay him a $3.375 million settlement and issued a public apology,” continued Thiessen.

Related: Not OK for Feds to Weaponize SPLC List to ‘Attack Citizens’

“The SPLC is a once-storied organization that did important work filing civil rights lawsuits against the Ku Klux Klan in the 1970s,” noted Thiessen. “But it has become a caricature of itself, labeling virtually anyone who does not fall in line with its left-wing ideology an “extremist” or “hate group.”

The SPLC’s actions matter because they amount to an assault on constitutional rights — an assault on every American’s freedoms.

Elizabeth Economou is a former CNBC staff writer and adjunct professor. Follow her on Twitter.

(photo credit, article image: David Horowitz, CC BY-SA 2.0, by Gage Skidmore)